1. Technical Field
The present invention relates to exercise and test apparatus for hip abduction, adduction, flexion and extension. More particularly, the present invention relates to a trunk stabilization device, for use with an existing exercise/test machine, that permits the desired muscles to be exercised/tested without interference from other muscles. In the particular embodiment described herein, the stabilization device is adapted for use with the Cybex II machine.
2. Description of the Prior Art
The generally accepted measurement criterion for the maximum tension which can be exerted by a muscle is the maximum moment of force that a muscle can exert on a body part. This is referred to as the maximum strength of the muscle and is expressed, for example, in kilograms per square centimeter of transverse section. In order to be meaningful, this measurement parameter must be expressed relative to the length of the muscle or the position of the body part. Several factors influence the validity of muscle strength tests. First, the muscle or muscle groups to be tested must be isolated from muscles which may contribute a moment to the measurement apparatus. This is accomplished by positioning the subject appropriately and stabilizing the parts of the body containing muscles which are not part of the measurement. Second, the moment or torque measuring device must be oriented perpendicular to the moment arm of the body. The measuring device must also operate in the plane of motion of the body. This requires a reasonable estimate of the axis of rotation of the body part involved.
Strength measurements should be taken at a proportional distance from the axis of rotation of the body part comparing measurements from different subjects. This is particularly important when the force exerted by the body part is the parameter to be measured. With respect to this methodology, moment measurements should also be taken at a proportional distance from the axis of rotation.
A widely used device for measuring strength and endurance of human muscles is a torque transducer called Cybex II, manufactured by Cybex, a division of Lumex, Inc., of Bay Shore, N.Y. This device is described in various catalogs printed by the manufacturer and also in U.S. Pat. No. 3,465,592 to Perrine, which patent is expressly incorporated herein, in its entirety, by this reference. In the Cybex II apparatus, muscular strength and endurance are measured as a function of the torque or moment applied by muscular exertion required to rotate an actuator shaft about its axis. The Cybex II is a passive component and does not apply force to the subject; it merely measures the torque applied to the device by the subject. A speed control unit permits the maximum rate of angular displacement of the input shaft to be set from zero degrees per second to two hundred ten degrees per second. When the speed control is set at zero degrees per second, the subject is able to apply torque to the input shaft but the input shaft does not rotate. This configuration is used to measure isometric strength of the muscle involved. When the speed control is set at values greater than zero degrees per second, the input shaft rotates, in response to applied torque from the subject, to a range of motion at a constant velocity for as long as the subject applies torque to the system. This latter configuration is employed to measure the concentric strength and muscular endurance of the subject.
The Cybex II is somewhat useful in exercising/testing hip abduction and hip flexion but is not at all useful for exercising/testing hip adduction and extension. One reason for this is that the user/subject is prone during the test and in a position to leverage his/her body weight to "lean into" the actuator with more than the muscles of interest. In addition, because of the capability of using body leverage, the subject can readily apply more torque to the torque transducer than it can safely accept, therby creating the possibility of permanent damage to the machine. For this reason, Cybex does not guarantee the proper functioning of the Cybex II for hip extension and adduction tests. Of course, testing hip flexion, extension, abduction and adduction while the subject is prone is also very unrealistic since such movements are rarely, if ever, attempted while prone. However, these muscular movements cannot be accurately exercised/tested on a Cybex II when the subject is standing upright because there is no means for stabilizing the subject's trunk to assure that only the muscles of interest are tested/exercised.